Adaptive immunity 2 Flashcards

1
Q

Describe the basics of lymphocyte activation, differentiation, memory and effector responses

A
  • antigen recognition - receptor has to recognise the antigen being presented to it by APC
  • if there are other stimulatory signals - T cells are activated
  • this causes secretion of IL-2R cytokine (main T cell growth factor)
  • acts as an autocrine loop - drives clonal expansion of antigen specific cell
  • also have differentiation of the responding cell - differentiate into a particular effector cell that actively performs its funtion
  • differentiate into memory cells
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2
Q

What is the 2 signal hypothesis for T cell activation?

A
  • co-stimulatory signals required for optimal T cell activation and proliferation
    • signal 1 - antigen-specific TCR engagament
    • signal 2 - contact with co-stimulatory ligands
      • signal 3 - cytokines directing T cell differentiation into distinct effectory cell types
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3
Q

What are the positive co-stimulatory receptors that facilitate activation and proliferation? (signal 2)

A
  • CD28
    • 44kDa glycoprotein homodimer - expressed on majority of T cells
    • binds to CD80 and CD86 expressed by APCs
    • initial activation events
  • ICOS
    • inducible co-stimulator
    • binds ICO-ligand on activated APCs
    • expressed on memory cells and effector T cells
    • help to maintain activity of already differentiated cells
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4
Q

What are the negative co-stimulatory receptors (help turn activation off)

A
  • CTLA-4
    • induced within 24 hours after after activation, peaks 2-3 days post-stimulation
    • binds to CD80/86 with higher affinity than CD28, but shuts down signaling pathways
  • PD-1
    • programme death 1 CD279 and BTLA
      • PD-1 - help to mediate T cell tolerance in non-lympoid tissues
      • BTLA - down regulate inflam and autoimmune responses
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5
Q

What is clonal anergy?

A
  • state of non-responsiveness
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6
Q

When does clonal anergy occur?

A
  • if a co-stimulatory signal is absent
  • helps to provide tolerance (especially in periphery)
  • if only 1 signal is recieved - cell in rendered nonresponsive
  • might happen if a T cell isnt screened against peripheral self-antigen during development
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7
Q

In T cell activation, what do the initial signals 1 and 2 induce?

A
  • up-regulation of pro-survival genes
  • transcription of IL-2 and IL-2R genes
  • IL-2 is an example of an autocrine type of cytokine response system
  • outcome is activation and robust proliferation
    • production of memory and effecrot clonal cell pops
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8
Q

Describe what happens during signal 3

A
  • depending on which cytokines are present as the T cell becomes activated, different outcomes can occur
  • cytokines can send the T cell down different subset development pathways
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9
Q

What are theb CD4 T cell distinct subsets?

A
  • Th1 and Th2
  • Th17
  • Treg
  • Tfh - (follicular)
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10
Q

How do PAMPs aid in T cell differentiation?

A
  • PAMPs bind to PRRs on the APC
  • different PPRs = different cytokines produced
    • viruses stimulate IL-12 to induce Th1 subsets
    • worms stimulate IL-4 to induce Yh2 subsets
  • this creates the cytokine evironment that drives the T cell down a pathway
  • APC detect PAMP (virus, bacteria etc)
  • produce a cytokine environment that drives the helper cell to become the most appropriare population to deal with infection
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11
Q
A
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